Different Strains Of Influenza Research Articles

Influenza vaccine effectiveness by age for Influenza A/B viruses between 2011-2020

Understanding whether influenza vaccine effectiveness (VE) varies by age is crucial to determine which populations need refinements in vaccination strategy or additional measures to reduce influenza rates, hospitalizations, and deaths. Our objective was to analyze the mean VE for different strains of influenza across five age groups: 6 months–8 years, 9–17 years, 18–49 years, 50–64 years, and 65+ years old. We used VE data for Influenza A, H3N2, and H1N1 strains, and Influenza B vaccines from the Centers for Disease Control and Prevention (CDC), collected between 2011–2020. We compared VE rates across different years, strains, and age groups. Overall, VE varied significantly by year, strain, and age group (p < 0.05, one-way ANOVA). The youngest age group (6 months–8 years) had a significantly higher VE than both the 18–49 years old and 65 years old or greater age groups (p<0.05, one-way ANOVA). Future vaccine development should be tailored to these two distinct populations to ensure adequate protection against influenza.

Designing multi-epitope mRNA construct as a universal influenza vaccine candidate for future epidemic/pandemic preparedness

Despite the availability of prevention and treatment strategies and advancing immunization approaches, the influenza virus remains a global threat that continues to plague humanity with unpredictable pandemics. Due to the unusual genetic variability and segmented genome, the reassortment between different strains of influenza is facilitated and the viruses continuously evolve and adapt to the host cell's immunity. This underlies the seasonal vaccine mismatches that decrease the vaccine efficacy and increase the risk of outbreaks. Thus, the development of a universal vaccine covering all the influenza A and B strains would reduce the pervasiveness of the influenza virus. In the current study, a potentially universal influenza multi-epitope vaccine was designed based on the experimentally tested conserved T cell and B cell epitopes of hemagglutinin (HA), neuraminidase (NA), nucleoprotein (NP), and matrix-2 proton channel (M2) of the virus. The immune simulation and molecular docking of the vaccine construct with TLR2, TLR3, and TLR4 elicited the favorable immunogenicity of the vaccine and the formation of stable complexes, respectively. Ultimately, based on the immunoinformatics analysis, the universal mRNA multi-epitope vaccine designed in this study might have a protection potential against the various subtypes of influenza A and B.

Infectivity versus fatality of SARS-CoV-2 mutations and influenza

ObjectivesBecause of the spread of the Omicron variant, many countries have experienced COVID-19 case numbers unseen since the start of the pandemic. We aimed to compare the epidemiological characteristics of Omicron with previous variants and different strains of influenza to provide context for public health responses.MethodsWe developed transmission models for SARS-CoV-2 variants and influenza, in which transmission, death, and vaccination rates were taken to be time-varying. We fit our model based on publicly available data in South Africa, the United States, and Canada. We used this model to evaluate the relative transmissibility and mortality of Omicron compared with previous variants and influenza.ResultsWe found that Omicron is more transmissible and less fatal than both seasonal and 2009 H1N1 influenza and the Delta variant; these characteristics make Omicron epidemiologically more similar to influenza than it is to Delta. We estimate that as of February 7, 2022, booster doses have prevented and Omicron infections in the United States and Canada, respectively.ConclusionOur findings indicate that the high infectivity of Omicron will keep COVID-19 endemic, similar to influenza. However, because of Omicron's lower fatality rate, our work suggests that human populations living with SARS-CoV-2 are most likely.

Punicalagin is a neuraminidase inhibitor of influenza viruses.

Influenza A virus (IAV) causes great morbidity and mortality worldwide every year. However, there are only a limited number of drugs clinically available against IAV infection. Further, emergence of drug-resistant strains can render those drugs ineffective. Thus there is an unmet medical need to develop new anti-influenza agents. In this study, we show that punicalagin from plants possesses strong anti-influenza activity with a low micromolar IC50 value in tissue culture. Using a battery of bioassays such as single-cycle replication assay, neuraminidase (NA) inhibition assay, and virus yield reduction assay, we demonstrate that the primary mechanism of action (MOA) of punicalagin is the NA-mediated viral release. Moreover, punicalagin can inhibit replication of different strains of influenza A and B viruses, including oseltamivir-resistant virus (NA/H274Y), indicating that punicalagin is a broad spectrum antiviral against both IAV and IBV. Further, although punicalagin targets NA like oseltamivir, it has a different MOA. These results suggest that punicalagin is an influenza NA inhibitor that may be further developed as a novel antiviral against influenza viruses.

Responses of human mast cells and epithelial cells following exposure to influenza A virus

As a part of innate immune defense, the role of mast cells during viral replication has been incompletely understood. In this study, we characterized and compared the responses of the human mast cell line, LAD2, and human lung epithelial cell line, Calu-3, against three influenza A virus strains; A/PR/8/34 (H1N1), A/WS/33 (H1N1) and A/HK/8/68 (H3N2). We found that there were strain-dependent mast cell responses, and different profiles of cytokine, chemokine and antiviral gene expression between the two cell types. All three strains did not induce histamine or β-hexosaminidase release in LAD2. A/HK/8/68 induced release of prostaglandin D2 in LAD2, whereas A/PR/8/34 and A/WS/33 did not. We found that, among those examined, only CCL4 (by A/PR/8/34) was statistically significantly released from LAD2 cells. Furthermore, there was increased mRNA expression of viral recognition receptors (RIG-I and MDA5) and antiviral protein, viperin, but levels and kinetics of the expression were different among the cell types, as well as by the strains examined. Our findings highlight the variability in innate response to different strains of influenza A virus in two human cell types, indicating that further investigation is needed to understand better the role of mast cells and epithelial cells in innate immunity against influenza A viruses.

Inactivation methods for whole influenza vaccine production.

Despite tremendous efforts toward vaccination, influenza remains an ongoing global threat. The induction of strain-specific neutralizing antibody responses is a common phenomenon during vaccination with the current inactivated influenza vaccines, so the protective effect of these vaccines is mostly strain-specific. There is an essential need for the development of next-generation vaccines, with a broad range of immunogenicity against antigenically drifted or shifted influenza viruses. Here, we evaluate the potential of whole inactivated vaccines, based on chemical and physical methods, as well as new approaches to generate cross-protective immune responses. We also consider the mechanisms by which some of these vaccines may induce CD8+ T-cells cross-reactivity with different strains of influenza. In this review, we have focused on conventional and novel methods for production of whole inactivated influenza vaccine. As well as chemical modification, using formaldehyde or β-propiolactone and physical manipulation by ultraviolet radiation or gamma-irradiation, novel approaches, including visible ultrashort pulsed laser, and low-energy electron irradiation are discussed. These two latter methods are considered to be attractive approaches to design more sophisticated vaccines, due to their ability to maintain most of the viral antigenic properties during inactivation and potential to produce cross-protective immunity. However, further studies are needed to validate them before they can replace traditional methods for vaccine manufacturing.

Insights into structural and inhibitory mechanisms of low pH-induced conformational change of influenza HA2 protein: a computational approach.

Though oseltamivir and zanamivir are the active anti-influenza drugs, the emergence of different strains of influenza A virus with mutations creates drug-resistance to these drugs. Therefore, it is essential to find a suitable approach to stop the viral infection. The present study focuses on understanding the conformational changes of the HA2 protein at different pH levels (pH7, pH6, pH5) and on blocking the low pH-induced conformational changes of the HA2 protein with a suitable ligand using molecular docking and molecular dynamics (MD) simulation methods. As the pH value decreases to pH5, the protein undergoes large conformational changes with less stability in the order of pH7 > pH6 > pH5. The fusion peptide (residues 1-20) and the extended loop (residues 58-75) deviate more at pH5. The ligand stachyflin bound between the N- and C-terminal helix regions retains the stability of the HA2 protein at pH5 and blocks the low pH-induced conformational transition. The performance of stachyflin is increased when it directly interacts with residues at the intramonomer binding site rather than the intermonomer binding site. The susceptibility of the HA2 protein of different subtypes to stachyflin is in the order of H1 > H7 > H5 > H2 > H3. Stachflin has a higher binding affinity for H1 (at pH7, pH6, pH5) and H7 subtypes than others. Lys47, Lys58, and Glu103 are the key residues that favor the binding and highly stabilize the HA2 protein at low pH. Graphical abstract Low pH-induced conformational change of influenza HA2 protein.

The role of RNA-RNA interactions in the assembly and reassortment of influenza A viruses

Influenza A virus has a genome consisting of 8 segments of negative sense RNA. When two influenza A virus strains infect the same cell, there is potential for the progeny to package segments from both strains. This process is termed reassortment and can lead to rapid genetic shifts that have previously generated strains of influenza responsible for pandemic events. Recent evidence suggests that assembly of the eight influenza genomic segments for packaging into a virion is mediated by RNA-RNA interactions between the segments. These interactions are likely to contribute to the varying compatibilities for reassortment observed between segments from different strains of influenza. We have captured complete RNA-RNA interaction maps for several influenza A viruses using a high-throughput sequencing approach and identify extensive, redundant, networks of RNA-RNA interactions between the genomic viral RNA segments. We extended this analysis to H1N1 and H3N2 reassortants, and found that by manipulating these interactions, we can drive preferential co-segregation of segments during reassortment. This work provides the first direct evidence that RNA-RNA interactions between the influenza virus genomic segments are a key factor in driving reassortment between viral strains.

Production and characterization of a conserved M2e peptide-based specific IgY antibody: evaluation of the diagnostic potential via conjugation with latex nanoparticles

Antibodies play an important role in combating and controlling viral diseases such as influenza. Immunoglobulin Y (IgY) antibodies have several advantages such as a less invasive manufacturing process, ease of isolation, higher affinity compared with IgG antibodies, and cost-effectiveness. To date, although specific IgY production has been performed for different strains of influenza A, to the best of our knowledge, an IgY against the M2e peptide has not been produced. In the current study, IgY antibodies are produced, purified, and characterized using the M2e peptide sequence for the first time with the intent to apply them for the diagnosis of influenza A virus. Anti-M2e IgY antibodies are obtained from eggs using a two-step purification method. The activity and characterization of the antibodies are determined using an enzyme-linked immunosorbent assay, a nano-spectrophotometer, an SDS-Page assay, and a Western Blot analysis. Finally, anti-M2e IgY antibodies are conjugated to the latex nanoparticles, and the reaction between the influenza A virus and the nanoparticles is demonstrated using light microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy. In conclusion, this study shows that anti-M2e IgY antibodies can contribute to the diagnosis, treatment, and prevention of the influenza A virus.

Susceptibility of influenza viruses to hypothiocyanite and hypoiodite produced by lactoperoxidase in a cell-free system.

Lactoperoxidase (LPO) is an enzyme found in several exocrine secretions including the airway surface liquid producing antimicrobial substances from mainly halide and pseudohalide substrates. Although the innate immune function of LPO has been documented against several microbes, a detailed characterization of its mechanism of action against influenza viruses is still missing. Our aim was to study the antiviral effect and substrate specificity of LPO to inactivate influenza viruses using a cell-free experimental system. Inactivation of different influenza virus strains was measured in vitro system containing LPO, its substrates, thiocyanate (SCN-) or iodide (I-), and the hydrogen peroxide (H2O2)-producing system, glucose and glucose oxidase (GO). Physiologically relevant concentrations of the components of the LPO/H2O2/(SCN-/I-) antimicrobial system were exposed to twelve different strains of influenza A and B viruses in vitro and viral inactivation was assessed by determining plaque-forming units of non-inactivated viruses using Madin-Darby canine kidney cells (MDCK) cells. Our data show that LPO is capable of inactivating all influenza virus strains tested: H1N1, H1N2 and H3N2 influenza A viruses (IAV) and influenza B viruses (IBV) of both, Yamagata and Victoria lineages. The extent of viral inactivation, however, varied among the strains and was in part dependent on the LPO substrate. Inactivation of H1N1 and H1N2 viruses by LPO showed no substrate preference, whereas H3N2 influenza strains were inactivated significantly more efficiently when iodide, not thiocyanate, was the LPO substrate. Although LPO-mediated inactivation of the influenza B strains tested was strain-dependent, it showed slight preference towards thiocyanate as the substrate. The results presented here show that the LPO/H2O2/(SCN-/I-) cell-free, in vitro experimental system is a functional tool to study the specificity, efficiency and the molecular mechanism of action of influenza inactivation by LPO. These studies tested the hypothesis that influenza strains are all susceptible to the LPO-based antiviral system but exhibit differences in their substrate specificities. We propose that a LPO-based antiviral system is an important contributor to anti-influenza virus defense of the airways.

A rapid-response ultrasensitive biosensor for influenza virus detection using antibody modified boron-doped diamond

According to the World Health Organization (WHO), almost 2 billion people each year are infected worldwide with flu-like pathogens including influenza. This is a contagious disease caused by viruses belonging to the family Orthomyxoviridae. Employee absenteeism caused by flu infection costs hundreds of millions of dollars every year. To successfully treat influenza virus infections, detection of the virus during the initial development phase of the infection is critical, when tens to hundreds of virus-associated molecules are present in the patient’s pharynx. In this study, we describe a novel universal diamond biosensor, which enables the specific detection of the virus at ultralow concentrations, even before any clinical symptoms arise. A diamond electrode is surface-functionalized with polyclonal anti-M1 antibodies, which then serve to identify the universal biomarker for the influenza virus, M1 protein. The absorption of the M1 protein onto anti-M1 sites of the electrode change its electrochemical impedance spectra. We achieved a limit of detection of 1 fg/ml in saliva buffer for the M1 biomarker, which corresponds to 5–10 viruses per sample in 5 minutes. Furthermore, the universality of the assay was confirmed by analyzing different strains of influenza A virus.

A Bayesian system to detect and characterize overlapping outbreaks

Outbreaks of infectious diseases such as influenza are a significant threat to human health. Because there are different strains of influenza which can cause independent outbreaks, and influenza can affect demographic groups at different rates and times, there is a need to recognize and characterize multiple outbreaks of influenza. This paper describes a Bayesian system that uses data from emergency department patient care reports to create epidemiological models of overlapping outbreaks of influenza. Clinical findings are extracted from patient care reports using natural language processing. These findings are analyzed by a case detection system to create disease likelihoods that are passed to a multiple outbreak detection system. We evaluated the system using real and simulated outbreaks. The results show that this approach can recognize and characterize overlapping outbreaks of influenza. We describe several extensions that appear promising.

LETHAL OUTCOMES IN INFLUENZA: CLINIC-PATHOLOGICAL APPROACH TO IMMEDIATE DEATH CAUSES

Influenza is one of the most outspread infections not seldom leading to lethal outcomes. Immediate death causes are analyzed rarely. Material and methods. We provided clinic-pathological correlations in 23 cases with lethal outcomes in 1999, 15 – in 2009, 31 in 2016 and 10 in 2017. Results. It was shown that in 2009 and 2017 most frequent lethal outcomes were related to bacterial superinfection in elderly people with severe background pathology. In 2009 and 2016 the leading role played respiratory distress syndrome predominantly in people of middle age, frequently with obesity. Conclusions: by circulation of different strains of influenza A virus the disease has substantial peculiarities. Lethal outcomes may be related: 1) severe respiratory insufficiency due to respiratory distress syndrome; 2) generalized viral infection; 3) secondary bacterial pneumonia; 4) aggravation of severe somatic diseases. Many aspects of pathogenesis need complex.study.

A spatial model of the efficiency of T cell search in the influenza-infected lung

Emerging strains of influenza, such as avian H5N1 and 2009 pandemic H1N1, are more virulent than seasonal H1N1 influenza, yet the underlying mechanisms for these differences are not well understood. Subtle differences in how a given strain interacts with the immune system are likely a key factor in determining virulence. One aspect of the interaction is the ability of T cells to locate the foci of the infection in time to prevent uncontrolled expansion. Here, we develop an agent based spatial model to focus on T cell migration from lymph nodes through the vascular system to sites of infection. We use our model to investigate whether different strains of influenza modulate this process.We calibrate the model using viral and chemokine secretion rates we measure in vitro together with values taken from literature. The spatial nature of the model reveals unique challenges for T cell recruitment that are not apparent in standard differential equation models. In this model comparing three influenza viruses, plaque expansion is governed primarily by the replication rate of the virus strain, and the efficiency of the T cell search-and-kill is limited by the density of infected epithelial cells in each plaque. Thus for each virus there is a different threshold of T cell search time above which recruited T cells are unable to control further expansion. Future models could use this relationship to more accurately predict control of the infection.

High immunogenicity of plant-produced candidate influenza vaccine based on the M2e peptide fused to flagellin

ABSTRACTThe ectodomain of the conserved influenza matrix protein M2 (M2e) is a promising target for the development of a universal influenza vaccines. Immunogenicity of M2e could be enhanced by its fusion to bacterial flagellin, the ligand for Toll-like receptor 5. Previously we reported the transient expression in plants of a recombinant protein Flg-4M comprising flagellin fused to 4 tandem copies of the M2e. The use of self-replicating recombinant vector based on the potato virus X allowed expression of Flg-4M in Nicotiana benthaminana leaves at a very high level, up to about 1 mg/g of fresh leaf tissue. Intranasal immunization of mice with Flg-4M induced M2e-specific serum antibodies and provided protection against lethal challenge with different strains of influenza A virus. Here we show that immunization with Flg-4M not only generates a strong immune response, but also redirects the response from the carrier flagellin toward the M2e epitopes. Significant IgG response to M2e was also developed in bronchoalveolar lavages of immunized mice. Protective activity of Flg-4M upon lethal influenza challenge correlated with a decrease of virus titers in lungs relative to the control. Overall these data show the potential for the development of a plant-produced M2e-flagellin universal influenza vaccine.

Supplementation of H1N1pdm09 split vaccine with heterologous tandem repeat M2e5x virus-like particles confers improved cross-protection in ferrets

Current influenza vaccines induce strain-specific immunity to the highly variable hemagglutinin (HA) protein. It is therefore a high priority to develop vaccines that induce broadly cross-protective immunity to different strains of influenza. Since influenza A M2 proteins are highly conserved among different strains, five tandem repeats of the extracellular peptide of M2 in a membrane-anchored form on virus-like particles (VLPs) have been suggested to be a promising candidate for universal influenza vaccine. In this study, ferrets were intramuscularly immunized with 2009 H1N1 split HA vaccine (“Split”) alone, influenza split vaccine supplemented with M2e5x VLP (“Split+M2e5x”), M2e5x VLP alone (“M2e5x”), or mock immunized. Vaccine efficacy was measured serologically and by protection against a serologically distinct viral challenge. Ferrets immunized with Split+M2e5x induced HA strain specific and conserved M2e immunity. Supplementation of M2e5x VLP to split vaccination significantly increased the immunogenicity of split vaccine compared to split alone. The Split+M2e5x ferret group showed evidence of cross-reactive protection, including faster recovery from weight loss, and reduced inflammation, as inferred from changes in peripheral leukocyte subsets, compared to mock-immunized animals. In addition, ferrets immunized with Split+M2e5x shed lower viral nasal-wash titers than the other groups. Ferrets immunized with M2e5x alone also show some protective effects, while those immunized with split vaccine alone induced no protective effects compared to mock-immunized ferrets. These studies suggest that supplementation of split vaccine with M2e5x-VLP may provide broader and improved cross-protection than split vaccine alone.

The Role of Hemagglutinin in Influenza Virus Transmission

Influenza is a rapidly mutating RNA virus causing mortality and morbidity in humans.The three different strains of influenza are characterized by different surface glycoproteins. Hemagglutinin (HA) is one of the primary binding proteins of Influenza A, the most prevalent strain of the virus. HA is a trimer, with each macromolecule consisting of a head and stalk region. The head region recognizes sialic acid on the host cell surface, initiating viral infection. The sialic acid binding site is highly susceptible to antigenic drift, and is the primary target of current vaccine development. The binding site consists of a loop‐helix‐loop region that allows for the attachment between HA and sialic acid. Because this region is both constantly mutating and strain specific, new vaccines need to be developed annually. Most antigenic drift is located within two antigenic sites. The Marshfield High School SMART (Students Modeling A Research Topic) Team will be modeling the sialic acid binding site on HA to demonstrate how the protein triggers viral infection. The stalk domain functions to mediate fusion of the viral and endosomal membranes. During this process, the domain undergoes extensive structural rearrangement. As such, the stalk domain is a more suitable vaccine target because it is conserved across strains and is not as susceptible to genetic drift. Therefore, emerging research has focused on the stalk region for more promising vaccinations, and maybe an eventual elimination of the need to develop a new vaccine every year. The Marshfield Research Foundation is currently studying influenza vaccine effectiveness and safety including the effects of repeated vaccination on immunity.

Antiviral activity of baicalin against influenza A (H1N1/H3N2) virus in cell culture and in mice and its inhibition of neuraminidase.

Scutellaria baicalensis Georgi, a Chinese herbal decoction, has been used for the treatment of the common cold, fever and influenza virus infections. In previous studies, we found that oral administration of baicalein resulted in the inhibition of influenza A virus replication in vivo, which was linked to baicalin in serum. However, the effective dose and underlying mechanisms of the efficacy of baicalin against influenza A virus have not been fully elucidated. In this study, the antiviral effects of baicalin in influenza-virus-infected MDCK cells and mice were examined. The neuraminidase inhibition assay was performed to investigate the mechanism of action of baicalin. In vitro results showed that baicalin exhibited a half-maximal effective concentration (EC50) of 43.3 μg/ml against the influenza A/FM1/1/47 (H1N1) virus and 104.9 μg/ml against the influenza A/Beijing/32/92 (H3N2) virus. When added to MDCK cell cultures after inoculation with influenza virus, baicalin demonstrated obvious antiviral activity that increased in a dose-dependent manner, indicating that baicalin affected virus budding. Baicalin had clear inhibitory effects against neuraminidases, with half-maximal inhibitory concentration (IC50) of 52.3 μg/ml against the influenza A/FM1/1/47 (H1N1) virus and 85.8 μg/ml against the influenza A/Beijing/32/92 (H3N2) virus. In vivo studies showed that an intravenous injection of baicalin effectively reduced the death rate, prolonged the mean day to death (MDD) and improved the lung parameters of mice infected with influenza A virus. These results demonstrate that baicalin acts as a neuraminidase inhibitor, with clear inhibitory activities that are effective against different strains of influenza A virus in both cell culture and a mouse model, and that baicalin has potential utility in the management of influenza virus infections.

Construction of recombinant adenoviral vector expressing genes of the conservative proteins M2 “ion channel” and nucleoprotein of influenza A virus

Influenza is a highly contagious disease and one of the most wide spreaded infection in the world. Influenza type A strains are of very great epidemiological significance. A high degree of genetic variability leads to constant modification in the antigenic structure of influenza virus. Therefore, current influenza vaccines require periodic updating of the composition of the strains. At present, it is important to develop a universal vaccine that could protect against different strains of influenza A virus and it is can be based on the conserved antigens of the virus. Recombinant adenoviral vectors expressing genes of conserved viral antigens may be used for a promising candidate vaccine against influenza A. Using a homologous recombination method, in this study we have developed a recombinant adenoviral serotype 5 vector that expresses the genes of the M2 ion channel and nucleoprotein (NP) of influenza A virus. The genes of the consensus sequences of the M2 protein and NP of human influenza A virus were inserted into the structure of the viral genome. The expression of the M2 and NP antigens using the recombinant adenovirus vector in a permissive line of eukaryotic cells was detected by Western blot assay. The high immunogenicity of the recombinant adenovirus vector obtained was demonstrated by intranasal immunization of laboratory mice.

Influenza infection results in local expansion of memory CD8+ T cells with antigen non-specific phenotype and function

Primary viral infections induce activation of CD8(+) T cells responsible for effective resistance. We sought to characterize the nature of the CD8(+) T cell expansion observed after primary viral infection with influenza. Infection of naive mice with different strains of influenza resulted in the rapid expansion of memory CD8(+) T cells exhibiting a unique bystander phenotype with significant up-regulation of natural killer group 2D (NKG2D), but not CD25, on the CD44(high) CD8(+) T cells, suggesting an antigen non-specific phenotype. We further confirmed the non-specificity of this phenotype on ovalbumin-specific (OT-I) CD8(+) T cells, which are not specific to influenza. These non-specific CD8(+) T cells also displayed increased lytic capabilities and were observed primarily in the lung. Thus, influenza infection was shown to induce a rapid, antigen non-specific memory T cell expansion which is restricted to the specific site of inflammation. In contrast, CD8(+) T cells of a similar phenotype could be observed in other organs following administration of systemic agonistic anti-CD40 and interleukin-2 immunotherapy, demonstrating that bystander expansion in multiple sites is possible depending on whether the nature of activation is either acute or systemic. Finally, intranasal blockade of NKG2D resulted in a significant increase in viral replication early during the course of infection, suggesting that NKG2D is a critical mediator of anti-influenza responses prior to the initiation of adaptive immunity. These results characterize further the local bystander expansion of tissue-resident, memory CD8(+) T cells which, due to their early induction, may play an important NKG2D-mediated, antigen non-specific role during the early stages of viral infection.